This invention relates to a rotating seal body for a face type seal, which may be unitized and which has an axial flexing membrane, and is more particularly directed to such a seal for use with a rotatable shaft and a fixed bore. Such seals are particularly useful for shafts carrying an impeller within a fluid filled housing such as may be found on a fluid pump.
One problem with prior art seals is that heat of friction generated by relative motion of the seal faces causes such seals to fail prematurely. Additionally, the structure of known prior art seals causes the sealing faces to address one another in a cam-like motion to keep the faces in sealing abutment, thus placing the seal under greater stress.
Another difficulty with some conventional seals is with the need to design into them a relatively high rate (lbs. per inch) compression spring. Such a prior art spring also has requirements for seating on a suitable surface against the membrane or bellows, and that structure must be built into the prior art seal.
In order for a face type seal to properly function, two surfaces, one rotating and the other stationary, must contact each other in sealing abutment. Regardless of the seal face materials employed, frictional heat due to relative motion is generated. Some of this heat can be dissipated into the medium being sealed. However, when the sealed medium is hot or not present, such as in periods of fluid aeration, dissipation of frictional heat is not possible. Many face type seals fail under such conditions because of seal face distortion or cracking.
In the present invention, a heat flow path is created from the stationary face through the heat conductive metal stamping which presses into the pump housing or its equivalent. The pump housing or its equivalent exhibits large surface areas and is generally constructed from a thermally conductive material which allows heat to flow away from the seal faces. This is especially true when pump cavitation occurs or there is a lack of the sealed medium. In the present invention, the stationary seal face is resiliently and sealingly positioned while maintaining the described heat transfer path.
It is known that fluid leakage between metal to metal press fits on to the pump shaft can occur due to lobbing or out-of-roundness. Generally, a penetrant type of sealant is applied to prevent such leakage. However, due to the low viscosity of such a sealant, it is not uncommon for the sealant to be deposited onto a seal face, thus impairing proper sealing. The present invention allows the resilient annular membrane of the seal to be positioned directly onto the shaft and maintain unitization of the sealing faces, and this is desirable, since the resiliency of this member conforms to lobbing or out-of-roundness creating a seal without the use of such additional sealants.
In normal face seal usage, it is not uncommon for one of the seal faces to be installed out of square or at a position which is not perpendicular to the shaft axis of rotation. When the resilient annular member is part of the stator and the rotating seal face is unsquare, it is necessary for the stator seal face to tilt axially to remain in sealing abutment. This tilting can be compared to a cam-like action and will occur at the speed of the shaft rotation. The mass of this seal face and its related components represents an inertia which must be moved during each rotation of the shaft. Lack of movement or a delay in the exact time of movement will cause the seal faces to part from sealing abutment. By positioning the resilient annular member on to the rotating shaft, the need for this cam-like motion is eliminated. When such a seal is mounted unsquare to the shaft axis of rotation, the resilient annular member allows the rotating face to assume a plane that conforms to the plane of the unsquarely mounted face. During shaft rotation, this plane is maintained and no cam-like motion of one of the seal faces is necessary to keep the faces in sealing abutment. By use of the present invention, the seal faces remain in abutment without objectionable cam-like motion and the work of maintaining abutment under such circumstances is eliminated, thus reducing wear and tear on the seal components.
In a seal embodying the present invention, a heat transfer path is built into the seal to dissipate the heat of friction generated by the relative motion of the seal faces before the heat damages the seal structure. This heat transfer path not only provides means for dissipating heat of friction, but also specifically directs heat being dissipated to portions of the seal where the heat can be readily conducted in a defined direction away from a heat reservoir which would normally build up at the seal faces and damage seal components. This directed path can be achieved by selecting one seal face of relatively high thermal conductivity and the other seal face of relatively low thermal conductivity and placing the seal face of high thermal conductivity in thermal conducting relation to a conductive mass which absorbs the heat to be dissipated.
Such a structure allows the resilient annular membrane of the seal to rest directly on the shaft, and such a position of the resilient annular member on the rotating shaft results in a fixed plane of rotation for the seal faces, even when the stationary face of the seal is not assembled perpendicularly to the axis of rotation of the shaft, thus eliminating the need for one of the faces of the seal to move in a cam-like motion for keeping the faces in sealing abutment, as described, which would be otherwise necessary.
By use of a face seal embodying the present invention, a low rate spring may be employed and such a spring does not require such critical seating as a prior art spring. Additionally, the present invention permits the use of positive drive features with rapid dissipation of heat, and the axial flexing membrane need not absorb the axial compression length of the spring, thus lengthening seal life.
In applications where a suitable surface to position a compression spring cannot be located and sealing directly on the shaft with a flexible axial sealing element is not required, a seal embodying the present invention can be packaged to utilize a finger spring as an alternative to a low rate spring, and such a finger spring is suitable to deliver an axial load to the seal faces. In any event, the axial flexing membrane is prepositioned and the seal face will rotate in a fixed plane regardless of the position of the non-rotating face and the compression on the spring.
Unitizing (providing a seal assembly where the stator and rotor portions are interconnected together) is also easily accomplished with a seal embodying the present invention, and such packaging can be achieved by providing a rolled lip or lugs on the rotor portion of the seal over which the stator portion is engaged.